REACTIVITY-RATE CONSTANT RATIO FOR SCAVENGERS OF CHARGED-PARTICLES IN NON-POLAR LIQUIDS

We have considered the reactions of electrons and positive holes with neutral scavenger molecules in nonpolar liquids. We have explicitly analyzed those cases where the yield G(P) of scavenged electrons or holes per 100 eV of ionizing radiation absorbed follows the empirical formula G(P) = Gfi + Ggi(αscs)1/2[1 + (αscs)1/2]-1, where cs is the scavenger concentration, Gfi and Ggi are the free ion yield and geminate ion yield, respectively, and αs is an empirical parameter, called the reactivity, which is characteristic of a given solvent-scavenger system. By combining this formula with the diffusion theory of Magee and Tayler, we have obtained for the ratio αs/ks the following formula: αs/ks = (rc2/D)(Gfi/Ggi)2. Here ks is the bimolecular rate constant for reaction of the electron or hole with the scavenger, D is the sum of the electron and hole diffusion coefficients, and rc = e2/εkT, where e is the charge of the electron, k is Boltzmann's constant, T is the absolute temperature, and ε is the liquid dielectric constant. For electron scavengers in cyclohexane, n-hexane, and isooctane, at T = 296 K, experimental values for αs/ks are known and are in satisfactory agreement with the ratio formula. For 14 other liquids at T = 296 K the formula predicts that αs/ks lies in the range of 0.04-155 ps. The formula also allows the temperature dependence of αs/ks to be assessed. For propane at T = 148, 183, and 230 K, we find αs/ks = 47, 0.7, and 0.1 ps, respectively. Although the ratio formula is specific to the representation of G(P) above, our method of derivation can be applied to any representation of G(P) so long as it is an analytic function of cs1/2. © 1979 American Chemical Society.